1. Field of the Invention
This invention relates to radiation backscatter imaging devices. In one aspect, this invention relates to x-ray backscatter imaging devices. In one aspect, this invention relates to in situ inspection of wellbore casings and pipelines. In one aspect, this invention relates to the use of radiation backscatter imaging devices for in situ inspection of wellbore casings and pipelines.
2. Description of Related Art
Scaling, corrosion, precipitates, and pipe and casing defects are all issues storage and pipeline operators face on a continual basis in managing the integrity of their production well and pipeline assets. These defects often lead to diminished deliverability, on the order of 5 to 20%, in production wells, casing integrity issues requiring costly remediation, pipeline integrity issues requiring repair or replacement, and potentially catastrophic failures which may result in serious injury or even fatalities. Conventional mineral scale formation, microbial induced corrosion, and material defect assessment and inspection processes in wellbores and pipelines are complicated, time-consuming, and very costly due to the range of operating conditions and existing inspection technologies. Thus, there is a need for wellbore and pipeline inspection devices which are less complicated, less time-consuming, and less expensive than conventional devices and which are able to operate in the extreme conditions inside wellbores and pipelines.
X-ray imaging techniques based on Compton backscatter enable inspection and screening of a wide variety of objects including vehicles, luggage, and even people. In contrast to more commonly used transmission images, backscatter imaging involves positioning both the radiation source and the detection apparatus on the same side of a target object.
Compton x-ray backscatter images are formed by scanning a pencil-shaped illumination beam of x-rays along one dimension of an object that is being inspected. At each position of the scanning pencil illumination beam, scattered x-rays are collected by large detectors placed on the same side of the system as the x-ray source. By tracking the instantaneous position of the pencil illumination beam on the target object and measuring the overall intensity of the scattered x-rays incident on the detectors, a scattered intensity can be associated with each beam position on the target object. The entire two-dimensional image can then be constructed by moving either the target object or the conveyance containing the x-ray source-detector combination in a direction perpendicular to the direction of the pencil beam scan. In this way, the target object can be scanned line by line.
To produce a continuous stream of data with substantially all of the parts of the target image showing, the x-ray source must produce either a continuous or high duty cycle fan beam output. To cover a reasonable field of view, the fan beam opening angle should also be large. To enable a pixel-by-pixel beam scan on the target, a moving collimator positioned in front of the fan beam with an opening designed to allow the desired size pencil beam through his required. As the collimator moves, different parts of the x-ray fan beam are selected by the collimator, with the effect of scanning the pencil beam in one dimension across the target. Conventionally, a rotating collimator rather than a reciprocating motion is used to provide this function. The resolution of the system is determined from a combination of the chopper wheel aperture, x-ray tube focal spot size, the size of the chopper wheel, and the distance to the object being scanned. The backscatter detectors, which are designed to collect the needed backscatter flux, play no role in the image resolution.